1. Technical Field of the Invention
The present invention relates to an apparatus for controlling automatic travel of a vehicle, and in particular, to the apparatus having a function of automatically shifting a stopped state of the vehicle to a traveling state thereof.
2. Related Art
In recent years, there is known an apparatus having a function of automatically controlling the torque generated by an on-vehicle motive power generator, in the case where a vehicle is in the process of transition from a stopped state to a traveling state.
This type of control apparatus is suggested, for example, in Japanese Patent Laid-Open Publication No. 2005-051886. In the apparatus suggested in this literature, the torque to be imparted to the drive wheels by the motor is determined in starting the vehicle. Specifically, the torque is determined either based on the value obtained by multiplying a torque that is the balance of the gravity acting in the backward-movement direction of the vehicle when the vehicle is started, with the distribution rate of the torque, or based on the value of the requested torque corresponding to the user's manipulation of the accelerator, whichever is larger. The distribution rate is set so as to become larger as the inverse rotational speed of the on-vehicle motor becomes higher. Thus, the apparatus suggested in this literature is so configured that the torque generated by the motor is increased in the case where the vehicle moves backward when the brakes are released by the user on an ascending slope. Owing to this configuration, the vehicle can be prevented from moving backward by a large extent even on an ascending slope.
In the control apparatus mentioned above, however, the torque imparted to the drive wheels immediately after release of the brakes will be insufficient to overcome gravity causing backward movement of the vehicle, and thus the vehicle resultantly moves backward. When the user manipulates the accelerator for this backward movement, the torque corresponding to the user's manipulation of the acceleration will be imparted to the drive wheels. However, if this torque is excessively large, the drive wheels will lock or skid on the road surface. During the locking or skidding, the vehicle may be brought into the traveling state as the vehicle starts displacing in the travel direction. However, no braking force that would balance the gravity applied in the backward-movement direction of the vehicle will be obtained, if the user again steps on the brakes in an attempt to control the vehicle speed. Thus, the vehicle may again move backward.
As explained above, it may sometimes be difficult to adequately bring a vehicle from a stopped state into a traveling state, depending on the user's operation of the vehicle.